Atomization of liquids and slurries is important for many systems. Particularly, atomization of fuels for combustion and gasification applications is a key step in attaining proper performance in such applications. Fuel that has been atomized into smaller particles typically enables more complete combustion, higher combustion temperatures, and better mixing of the fuel with air so as to increase combustion efficiency.
Primarily, two types of atomizers are in use today: (1) high pressure single-fluid atomizers (shown in FIG. 1) and (2) dual-fluid atomizers (shown in FIGS. 2A, 2B and 3). In the high pressure single-fluid atomizers, a liquid or slurry fuel is pressurized to an elevated pressure which propels the fuel at high kinetic energy through an orifice into a nozzle injector. The atomized fuel leaving the nozzle injector is then sprayed into a combustor chamber. The high velocity of the fuel spray in turn provides for better mixing of the fuel and air and results in more efficient combustor performance.
A high pressure single-fluid atomizer as shown in FIG. 1 employs a high pressure pump to raise the pressure of the liquid fuel and to drive the atomizer. The pressurized fluid expands through the nozzle so as to impart a high velocity to the fluid, resulting in an atomized spray. The pump operation may be continuous or intermittent, with intermittent pumps being employed for fuel-injected internal combustion piston applications such as diesel and gasoline engines.
In dual-fluid atomizers, a separate atomization fluid is employed to achieve atomization of the liquid or slurry fuel. Generally, dual-fluid atomizers are either internally mixed as shown in FIGS. 2A and 2B or externally mixed as shown in FIG. 3. In internally mixed, dual-fluid atomizers, the atomizing fluid meets the fuel within an atomization chamber and the mixture is ejected at high velocity from a nozzle to form the atomized fuel spray. One such dual-fluid atomizer shown in FIG. 2A employs a Y-jet design where the atomization fluid (generally gas or steam) meets the liquid or slurry fuel at an acute angle. Another dual-fluid atomizer shown in FIG. 2B employs an eductor T-jet design where the atomization fluid flow meets the liquid or slurry fuel at a right angle. Such atomizers may operate as eductors and, in some applications, no pump is required for fuel introduction. In both of the internally mixed, dual-fluid atomizers described, mixing of the atomization fluid and the liquid or slurry fuel occur internally within the body of the atomizer before the atomized fuel spray leaves the atomizer.
In externally mixed, dual-fluid atomizers such as the one shown in FIG. 3, the atomizing fluid meets the liquid or slurry fuel outside the body of the atomizer. Mixing of the atomization fluid with the fuel outside the atomizer is particularly useful when coal slurries and viscous liquid fuels such as residual oils are employed. Such highly abrasive or highly viscous fuels tend to cause rapid erosion of the inner surfaces of the atomizer when an internally mixed atomizer is employed. By mixing the atomization fluid and fuels outside the body of the atomizer, rapid erosion is lessened.
In the particular externally mixed, dual-fluid atomizer shown in FIG. 3, an annular cavity distributes the liquid fuel or slurry around a supersonic jet of atomizing fluid. A film of liquid fuel is sheared by the supersonic flow of the atomizing fluid through the cavity to produce an atomized fuel spray. Fuel enters into the path of an atomization fluid after the atomization fluid exits from a supersonic nozzle. The atomization fluid is provided with sufficient velocity to sheer the fuel droplets into an acceptable atomized fuel spray.
As previously mentioned, high pressure, single-fluid atomizers are generally employed in diesel engines and similar fuel-injection applications, particularly when the flow rate profile versus time is to be controlled. Pressures employed in such single-fluid atomizers can be in excess of 10,000 pounds per square inch.
Where large power plants and boilers are involved, dual-fluid atomizers are generally preferred. Liquid fuel in such applications need not be pressurized to high levels, with pressures in the range of from about 50 to about 250 pounds per square inch being acceptable.
In each of the dual-fluid systems previously described, the atomization fluid typically employed is a compressible fluid such as air or steam. In compressed air systems, pressures in the range of from about 20 to about 180 pounds per square inch are generally used. Where steam is employed, the pressure range is generally from about 50 pounds per square inch to about 600 pounds per square inch depending on the application requirements.
With respect to the internally mixed atomizers, the ratio of atomization fluid to liquid fuel varies from about 0.07 to about 0.50 pounds of atomization fluid per pound of liquid fuel being atomized. For the externally mixed, dual-fluid atomizers, more atomization fluid flow is required. The amount of atomization fluid in such atomizers ranges from about 0.40 to about 3.0 pounds per pound of liquid fuel being atomized.
As may be expected with such prior art atomizers, a large amount of parasitic power is consumed by the air compressors to supply the atomization fluid. Although in internally mixed dual-fluid atomizers, as little as 1.5% of the entire plant output comprises the parasitic air power, externally mixed, dual-fluid atomizers typically require as much as 15% of total power plant output to operate the compressors. Moreover, as more viscous and more abrasive fuels are employed, the amount of air required for atomization increases substantially. In addition, large amounts of atomization air are required, particularly in the externally mixed atomization processes, resulting in the need for enormous compressors which require a significant portion of plant output for operating.
In summary, typical prior art atomizers require large amounts of compressed air or other fluid for atomization. Moreover, the internally mixed, dual-fluid atomizers often incur erosion problems. Accordingly, an efficient, non-eroding atomization process which does not require a substantial amount of parasitic power is needed.
The apparatus and processes according to the present invention overcome most, if not all, of the above-noted problems of the prior art and generally possess the desired attributes set forth above by using a pulse combustion apparatus to atomize fuels. The present atomization apparatus may be designed to supply atomized fuel to combustion, gasification, and other systems which employ atomized liquid or slurry streams.